Exacting SNG-probe measurements

For some years the Department of Electrophysics has measured Spectral Natural Gamma-ray logs (SNG-logs) in shallow boreholes (to 600 m below surface). For the interpretation - i.e. the ''transformation'' of count rates to concentrations of radioactive elements - there have been developed simple physical models and advanced computer models based on basic physical principles, and there have been performed a number of calibration measurements in order to check the computer models. For cased boreholes with thick layers of backfill it has been difficult (and expensive) to perform calibration measurements. In december 1991 the Department got an opportunity for performing special calibration measurements in a ''synthetic borehole'' - cased and supplied with a thick layer of backfill - that had been built for another purpose (than calibration of SNG-probes). The measurements and the results are described in this report, and the models mentioned above and some counting statistical problems, are briefly explained. (au)